Low profile inductors for high density circuit boards

ABSTRACT

An inductor includes a core formed of a magnetic material and a foil winding wound at least partially around or through at least a portion of the core. A first end of the winding extends away from the core to form an extended output tongue configured and arranged to supplement or serve as a substitute for a printed circuit board foil trace. A second end of the winding forms a solder tab. At least a portion of the extended output tongue and the solder tab are formed at a same height relative to a bottom surface of the core. Another inductor includes a core formed of a magnetic material, a winding wound at least partially around or through at least a portion of the core, and a ground return conductor attached to the core. The core does not form a magnetic path loop around the ground return conductor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 12/507,751 filed Jul. 22, 2009, now U.S. Pat. No. 8,040,212which is incorporated herein by reference.

FIELD

The present document relates to the field of low profile inductor designfor high-density printed circuit boards. In particular, the documentrelates to a low profile inductor suitable for use beneath processorheat sinks and in other areas where conventional inductors may interferewith other components.

BACKGROUND

Many high density printed circuit board assemblies (PCBs) are installedin tight housings, or have bulky components attached to them, such thatcomponent height in portions of the PCB must be limited. For example, inthe area near a processor of a personal computer motherboard, componentheight must be limited to avoid mechanical interference with processorheat sinks. Similarly, high profile components on PCMCIA or Cardbusdevices are undesirable because they may require the device to occupytwo slots in a laptop computer's connector instead of a single slot;occupancy of multiple slots may limit further system expandability andmay prevent use with machines having only a single slot available.

Voltage regulated down-converters for providing power to microprocessorintegrated circuits of laptop and desktop personal computers are known.Such converters typically include one or more inductors.

SUMMARY

In an embodiment, an inductor for assembly on a printed circuit boardincludes a core formed of a magnetic material and a first foil windingwound at least partially around or through at least a portion of thecore. A first end of the first winding extends away from the core toform a first extended output tongue, and a second end of the firstwinding forms a solder tab. The solder tab and at least a portion of thefirst extended output tongue are formed at a same height relative to abottom surface of the core for surface mount attachment to the printedcircuit board. The first extended output tongue is configured andarranged to supplement or serve as a substitute for a first foil tracedisposed on a surface of the printed circuit board.

In an embodiment, an inductor for assembly on a printed circuit boardincludes a core formed of a magnetic material, a first winding wound atleast partially around or through at least a portion of the core, and afirst ground return conductor attached to the core. The first windingand the first ground return conductor are configured and arranged suchthat inductance of the first ground return conductor is notsignificantly increased by presence of the core, while inductance of thefirst winding is significantly increased by presence of the core,relative to an otherwise identical inductor without the core.

In an embodiment, an inductor for assembly on a printed circuit boardincludes an elongated ground return conductor forming at least onesolder tab at each end of the conductor. The inductor further includesat least two spacer elements disposed on the ground return conductor andan elongated foil winding forming at least one solder tab at each end ofthe winding. The winding is disposed on the spacer elements such thatthe spacer elements separate the ground return conductor from thewinding to create a channel between the ground return conductor and thewinding.

In an embodiment, a printed circuit board assembly has a drop-ininductor attached to a printed circuit board. The drop-in inductorincludes a first foil winding wound through an opening in a magneticcore and a first ground return conductor attached to the core. The firstfoil winding and the first ground return conductor are configured andarranged such that inductance of the first ground return conductor isnot significantly increased by presence of the core, while inductance ofthe first foil winding is significantly increased by presence of thecore, relative to an otherwise identical inductor without the core. Thefirst foil winding and the first ground return conductor have endsformed as solder tabs for attachment to the printed circuit board, andthe tabs of the first foil winding and the first ground return conductorare formed at a same height relative to a bottom surface of the core.The tabs of the first foil winding and the tabs of the first groundreturn conductor are attached to foil of the same layer of the printedcircuit board. The printed circuit board forms an aperture, and the coreof the inductor extends into the aperture.

In an embodiment, a printed circuit board assembly includes a printedcircuit board, at least one switching device attached to the printedcircuit board, and an inductor attached to the printed circuit board.The inductor includes a core formed of a magnetic material and a foilwinding wound at least partially around or through at least a portion ofthe core. A first end of the winding extends away from the core to forman extended input tongue. At least a portion of the extended inputtongue is soldered to and supplements a first foil trace disposed on anouter surface of the printed circuit board, where the first foil traceelectrically couples the at least one switching device to the first endof the winding.

In an embodiment, a printed circuit board assembly includes a printedcircuit board, at least one switching device attached to the printedcircuit board, and an inductor attached to the printed circuit board.The inductor includes a core formed of a magnetic material and a foilwinding wound at least partially around or through at least a portion ofthe core. A first end of the winding is electrically coupled to the atleast one switching device, and a second end of the winding extends awayfrom the core to form an extended output tongue. At least a portion ofthe extended output tongue is soldered to and supplements a first foiltrace disposed on an outer surface of the printed circuit board.

In an embodiment, an inductor for assembly on a printed circuit boardincludes a core formed of a magnetic material and a winding. The corehas a first side and a second side opposite to the first side. A linearseparation distance between the first and second sides of the coredefines a length of the core. The winding includes (a) a core windingportion wound through the core, (b) a foil input tongue at the firstside of the core and extending away from the core in the lengthwisedirection, and (c) a foil output tongue at the second side of the coreand extending away from the core in the lengthwise direction. At least aportion of the foil input tongue and the foil output tongue are formedat a same height relative to a bottom surface of the core for surfacemount attachment to the printed circuit board, where the height isgenerally perpendicular to the lengthwise direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a PRIOR ART cross section of a motherboard.

FIG. 2 is a schematic of a PRIOR ART motherboard.

FIG. 3 shows a side plan view of one inductor installed on a PCB,according to an embodiment.

FIG. 4 shows a top plan view of the inductor of FIG. 3.

FIG. 5 shows a side plan view of another embodiment of the inductor ofFIG. 3 installed on a PCB.

FIG. 6 shows a side plan view of yet another embodiment of the inductorof FIG. 3 installed on a PCB.

FIG. 7 shows a top plan view of the inductor of FIG. 6.

FIG. 8 shows a side plan view of one inductor including ground returnconductors installed on a PCB, according to an embodiment.

FIG. 9 shows a top plan view of the inductor of FIG. 8.

FIG. 10 shows a top perspective view of the inductor of FIGS. 8 and 9with a magnetic core removed.

FIG. 11 shows a top plan view of one PCB footprint for use with theinductor of FIGS. 8-10, according to an embodiment.

FIG. 12 is a side plan view of another embodiment of the inductor ofFIG. 8 installed on a PCB.

FIG. 13 is a top plan view of the inductor of FIG. 12.

FIG. 14 is a top perspective view of the inductor of FIGS. 12 and 13with a magnetic core removed.

FIG. 15 shows a side plan view of yet another embodiment of the inductorof FIG. 8 installed on a PCB.

FIG. 16 shows a top plan view of the inductor of FIG. 15.

FIG. 17 shows a top perspective view of inductor of FIGS. 15 and 16.

FIG. 18 shows a top plan view one coupled inductor including extendedoutput tongues, according to an embodiment.

FIG. 19 shows a top perspective view of one winding of the inductor ofFIG. 18.

FIG. 20 shows a top perspective view of another embodiment of theinductor of FIG. 18.

FIG. 21 shows a top plan view of one coupled inductor including groundreturn conductors and extended input and output tongues, according to anembodiment.

FIG. 22 shows a top plan view of an embodiment of the coupled inductorof FIG. 21 including an isolator.

FIG. 23 shows a side plan view of the inductor of FIG. 22.

FIG. 24 shows a top plan view of one coupled inductor including groundreturn conductors and extend output tongues, according to an embodiment.

FIG. 25 shows a side plan view of the coupled inductor of FIG. 24installed on a PCB.

FIG. 26 is a top perspective view of the coupled inductor of FIGS. 24and 25.

FIG. 27 shows a top plan view of one coupled inductor including groundreturn conductors and extended output tongues, according to anembodiment.

FIG. 28 shows a side plan view of the coupled inductor of FIG. 27installed on a PCB.

FIG. 29 shows a side plan view of one inductor having a low profileinstalled on a PCB, according to an embodiment.

FIG. 30 shows a top plan view of the inductor of FIG. 29.

FIG. 31 shows a top perspective view of the inductor of FIGS. 29 and 30with isolators removed.

FIG. 32 shows one PCB footprint for use with the inductor of FIGS.29-31, according to an embodiment.

FIG. 33 shows a side plan view of one inductor having a low profileinstalled on a PCB, according to an embodiment.

FIG. 34 shows a top plan view of the inductor of FIG. 33.

FIG. 35 shows a top perspective view of the inductor of FIGS. 33 and 34with magnetic sections removed.

FIG. 36 shows a side plan view of one inductor having a low profileinstalled on a PCB, according to an embodiment.

FIG. 37 shows a top plan view of the inductor of FIG. 36.

FIG. 38 shows a top perspective view of the inductor of FIGS. 36 and 37with magnetic sections removed.

FIG. 39 shows a side cross-sectional view of a PRIOR ART drop-ininductors installed in a PCB aperture.

FIG. 40 shows a top plan view of the inductor of FIG. 39 installed in aPCB aperture.

FIG. 41 shows a top plan view of a plurality of PRIOR ART drop-ininductors installed in respective PCB apertures.

FIG. 42 shows a side cross-sectional view of one drop-in inductorincluding ground return conductors installed in a PCB aperture,according to an embodiment.

FIG. 43 shows a top plan view of the inductor of FIG. 42 installed in aPCB aperture.

FIG. 44 shows a top perspective view of the inductor of FIGS. 42 and 43.

FIG. 45 shows a top perspective view of the inductor of FIGS. 42-44 witha magnetic core removed.

FIG. 46 shows a top perspective view of one drop-in inductor includingground return conductors, according to an embodiment.

FIG. 47 shows an exploded perspective view of the inductor of FIG. 46with a magnetic core removed.

FIG. 48 shows a top perspective view of another embodiment of theinductor of FIGS. 46-47.

FIG. 49 shows an exploded perspective view of the inductor of FIG. 48with a magnetic core removed.

FIG. 50 shows a top perspective view of one drop-in coupled inductorincluding ground return conductors, according to an embodiment.

FIG. 51 shows a top perspective view of the inductor of FIG. 50 with amagnetic core removed.

FIG. 52 shows a top plan view of one PCB assembly including anembodiment of the inductor of FIGS. 50-51.

FIG. 53 shows a top perspective view of one N-winding coupled inductorincluding a ground return structure, according to an embodiment.

FIG. 54 shows a top perspective view of the windings of the inductor ofFIG. 53.

FIG. 55 shows a top perspective view of the ground return structure ofthe inductor of FIG. 53.

FIG. 56 shows an embodiment of the inductor of FIG. 53 installed in aPCB.

FIG. 57 shows an alternate embodiment of the inductor of FIG. 53.

FIG. 58 shows a top perspective view of one N-winding coupled inductorincluding a ground return structure, according to an embodiment.

FIG. 59 shows a top perspective view of one winding of the inductor ofFIG. 58.

FIG. 60 shows an embodiment of the inductor of FIG. 58 installed in aPCB.

FIG. 61 shows an alternate embodiment of the inductor of FIG. 58.

FIGS. 62-64 respectively show a perspective, a side plan, and a top planview of an inductor including two extended tongues, according to anembodiment.

FIGS. 65-67 respectively show a perspective, a side plan, and a top planview of an embodiment of the inductor of FIGS. 62-64 including groundreturn conductors.

FIG. 68 shows a perspective view of an inductor similar to the inductorFIGS. 65-67, according to an embodiment.

FIG. 69 shows a perspective view of an inductor similar to the inductorof FIGS. 62-64, according to an embodiment.

FIG. 70 shows a perspective view of another inductor similar to theinductor of FIGS. 65-67, according to an embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

It is noted that, for purposes of illustrative clarity, certain elementsin the drawings may not be drawn to scale. Specific instances of an itemmay be referred to by use of a numeral in parentheses (e.g., winding1802(1)) while numerals without parentheses refer to any such item(e.g., windings 1802).

In a high density printed circuit board assembly, such as a processormotherboard 100 assembly (FIG. 1) as used in a personal computer, theremay be portions of the assembly where circuit height is restricted, yetdevices in or near these areas may require considerable power. Forexample, motherboard 100 assembly may have a multilayer printed circuitboard 102 with an attached processor 103 in a processor socket 104.Since processor 103 may dissipate considerable power—in some casesexceeding a hundred watts at peak computer performance—a heat sink andfan assembly 106 is attached to processor 103 to cool processor 103.Heat sink and fan assembly 106 is often a large, bulky, device requiringa considerable keep-out zone 120 beneath it where only low-profilecomponents are allowed on motherboard 100 to prevent components onmotherboard 100 from mechanically interfering with heat sink and fanassembly 106.

In some systems, heat sink and fan assembly 106 may actually occupy onlysome of the space shown; however a system manufacturer may have reserveda larger volume to allow air to flow into the heat sink, and to allowfor future use of a different heat sink or fan with future, faster, andeven more power-hungry, processors. In other systems and subsystems,such as PCMCIA or CARDBUS cards, height restrictions may derive fromother factors such as overall card or system dimensions. Further,component height is strictly limited in laptop systems because ofdesires to limit machine thickness.

Processor 103 draws considerable current since much of the power itconsumes is at a low “core” voltage, typically between one and twovolts, although voltage at the processor's “periphery” may be higher.The “core” voltage is typically provided by an on-board DC-to-DCdown-converter. The DC-to-DC converter has one or more inductors, suchas inductor 110, as well as several capacitors 112. Inductor 110 oftenhas height 114 that would interfere with heat sink and fan assembly 106if inductor 110 were located under heat sink and fan assembly 106.Inductor 106 is therefore located some distance away from processorsocket 104. Similar situations may also arise with high performancegraphics chips as these also consume considerable power and oftenrequire heat sinks.

A schematic diagram (FIG. 2) illustrates the resulting problem ofparasitic impedance. Down-converter 202 is, in this example, amultiphase buck converter having switching devices 204 that rapidlyalternate a connection to each of several phase inductors 206 between apowered, a grounded, and an unpowered state. Switching devices 204connect to respective phase inductors 206 via respective switching nodes(Vx) 216. Current builds in each phase inductor 206 when it is powered,and decays when it is grounded. Output voltage and current are afunction of the percentage of time that each phase inductor 206 ispowered. Phase inductors 206 may be magnetically coupled, as shown inFIG. 2.

Output terminals of the phase inductors 206 are coupled together and tocapacitors 208 and processor 210 via an output node (Vo) 218. If theconnection from phase inductors 206 to capacitor 208 and processor 210is made only via a typical thin foil PCB trace (e.g., trace 116 FIG. 1),significant unintended, parasitic, impedances 212 may exist betweenprocessor 210, capacitor 208, and converter inductors 206. Impedances212 may have an inductive and a resistive component.

The low processor voltage, typically between one and two volts, and highprocessor current, often reaching peak currents of fifty to one hundredamperes, make the system quite sensitive to what may seem quite lowparasitic impedances 212. For example, a current of one hundred amperesin a two-milliohm parasitic impedance is sufficient to provide a twohundred-millivolt drop; at a one volt core voltage, this may representtwenty percent of operating voltage. Such voltage drop due to thehundred amperes also relates to twenty watts of conduction loss and isenvironmentally undesirable, as this conduction loss represents powernot used in the circuit, but is power used to produce heat wasted in theboard layout.

It is desirable to minimize impedances 212, since these may not onlywaste power, but may allow processor 210 voltage to deviate outsidedesirable operating limits. The same arguments apply to parasiticimpedances 214 between inductors 206 and power semiconductors 204, it isdesirable to minimize these impedances also.

To minimize parasitic resistances in inductors 206, these inductors areoften wound with one or just a few turns of thick foil (i.e., aconductive material such as copper having at least a substantiallyrectangular cross-section) or wire around or inside a powdered iron,ferrite, or similar ferromagnetic core suitable for use at the highfrequencies—in the range 20 kHz to above 1 MHz—at which switchingdevices 204 typically operate. Multiple inductors 206 are often used,their outputs being connected in parallel and operated as a multiphaseconverter, to handle the requisite current. The foil with whichinductors 206 are wound is typically significantly thicker than foilused for traces 116 on the PCB. In the embodiment of FIG. 1, the foil ofthe inductor extends, typically downwards and often wrapping under thecore, to form a solder tab 122 that connects to foil of PCB traces 116.

FIG. 3 shows a side plan view of one inductor 300 installed on a PCB302, and FIG. 4 shows a top plan view of inductor 300. Inductor 300, forexample, is used to at least partially solve one or more of the problemsdiscussed above, and inductor 300 may be used in DC-to-DC converterapplications (e.g., as a buck converter output inductor). Inductor 300includes at least one electrically conductive winding 304 wound at leastpartially around or through at least a portion of a magnetic core 306.For example, winding 304 may be wound through an opening in core 306,such as shown in FIGS. 3 and 4, where dashed lines indicate the outlineof winding 304 where obscured core 306. Core 306 is, for example, formedof a ferrite and/or powdered iron material, and may consist of one ormultiple magnetic elements. In an embodiment, winding 304, for example,is a single turn “staple” foil winding, thereby helping to minimizewinding length and resistance.

Inductor 300 further includes an extended output tongue 308 extendingaway from core 306. Extended output tongue 308 has a thickness similarto that of winding 304, and extended output tongue 308 is electricallycoupled to one end of winding 300. Extended output tongue 308 is, forexample, an extension of winding 304—such configuration may helpsimplify construction of inductor 300 and/or reduce combined resistanceof winding 304 and extended output tongue 308. At least a portion ofextended output tongue 308 is configured for attaching (e.g., soldering)to a foil PCB trace or solder pad. Although extended output tongue 308is shown as having a width 402 which is the same as a width 404 of theportion of winding 304 that passes through or at least partially aroundcore 306, widths 402 and 404 may differ. For example, width 402 may begreater than width 404 to help minimize impedance of extended outputtongue 308. In motherboard applications, extended output tongue 308 istypically electrically coupled to an output node (e.g., a buck converteroutput node). However, inductor 300 is not limited to such uses. Forexample, extended output tongue 308 could couple to a power supplyintermediate node.

Inductor 300 further includes a solder tab 310 electrically coupled tothe other end of winding 304, for soldering to a foil PCB solder pad. Inmotherboard applications, solder tab 310 is typically coupled to aninput node (e.g., a switching node in a buck converter). In alternativeembodiments, solder tab 310 could alternately be replaced by a differenttype of connector, such as a through-hole pin.

At least a portion of extended output tongue 308 and solder tab 310 are,for example, formed at the same height relative to a bottom surface 316of core 306 to facilitate surface mount connection of inductor 300 to aPCB. Some of such embodiments are capable of being placed on a PCB usingpick-and-place equipment and soldered to traces or solder pads of thePCB using reflow soldering techniques (e.g., infrared reflow, hot gasconvection, vapor phase reflow) or wave soldering techniques.

In some embodiments, solder tab 310 is replaced with an extended inputtongue. For example, FIG. 5 shows a side plan view of one inductor 500installed on PCB 302. Inductor 500 is an embodiment of inductor 300where solder tab 310 has been replaced with an extended input tongue502. At least respective portions of extended output tongue 308 andextended input tongue 502 are, for example, formed at the same heightrelative to bottom surface 316 of core 306 to facilitate surface mountconnection of inductor 500 to a PCB. Extended input tongue 502 is, forexample, an extension of winding 304. Extended input tongue 502typically has mechanical characteristics (e.g., width, thickness)similar to that of extended output tongue 308. However, extended inputtongue 502 is shorter in most embodiments of inductor 500 than extendedoutput tongue 308 because switching devices are typically located nearcore 306 of inductor 500.

Extended output tongue 308 may be used to provide a low impedanceelectrical connection to inductor 300. For example, extended outputtongue 308 may be configured and arranged for supplementing a foil PCBtrace connected to inductor 300. In some embodiments, at least a portionof extended output tongue 308 is formed for soldering to and extendingalong a foil trace on a PCB outer surface, thereby serving as aconductor in parallel with the trace. Extended output tongue 308typically has a thickness that is much greater than that of the PCBtrace—accordingly, extended output tongue 308 typically has a much lowerelectrical and thermal impedance than the PCB trace. Extending extendedoutput tongue 308 along a PCB trace to supplement the trace maysignificantly lower the trace's effective impedance, thereby reducingvoltage drop and power loss in the trace, as well as improving thetrace's heat sink ability. As another example, extended output tongue308 may be used in place of a PCB trace to provide a low impedanceelectrical connection to one end of winding 304, and thereby free up aPCB layer for other uses, such as to route signal traces. Similarly,extended input tongue 502 (FIG. 5) may also supplement or be used inplace of a PCB trace to provide a low impedance electrical connection towinding 304.

Extended output tongue 308 may also serve as a heat sink, therebyhelping to cool inductor 300 and a PCB that tongue 308 is attached to.Extended output tongue 308 also typically has a low profile, which mayadvantageously allow use of rework equipment, pick and place equipment,and/or test probes in the vicinity of tongue 308. Furthermore, becauseextended output tongue 308 is part of inductor 300, extended outputtongue 308 may withstand pressure from hot air rework equipment withoutbeing blown off a PCB.

In typical embodiments, winding 304 and extended output tongue 308 areformed of copper foil, such as between three and five millimeters wide,and from two tenths to one half millimeter thick. It is desirable forwidth 402 of extended output tongue 308 to be at least 1 millimeter topromote low impedance of tongue 308. The foil winding material typicallyused for winding 304 and extended output tongue 308 is substantiallythicker than typical PCB copper foils (e.g., trace 116, FIG. 1) becausehalf-ounce copper foil, as is typically used in PCB layers requiringfine lines, is approximately eighteen thousandths of a millimeter thick.Even three ounce copper foil, which may be used on special-purpose powerand ground-plane layers, is only about a tenth of a millimeter thick.Since direct-current sheet-resistivity of a copper conductor isinversely proportional to its thickness, the sheet-resistivity ofextended output tongue 308 may be as little as one-fiftieth that of abare PCB trace of equivalent length and width. Extended output tongue308 typically has length 406 of at least one centimeter to bridge adistance between inductor 300 and another component or portion of a PCB.However, extended output tongue 308 could be significantly shorter(e.g., two millimeters) if it only needs to run a short distance.Inductors including shorter extended tongues are typically easier tomanufacture and assemble than inductors including longer extendedtongues.

FIG. 3 shows one possible use of inductor 300 in an application having aheight restriction 312 (e.g., due to a heat sink assembly). In theexample of FIG. 3, inductor 300 is connected between a DC-to-DCconverter (e.g., buck converter) switching node Vx (e.g., node 216, FIG.2), and a converter output node Vo (e.g., node 218, FIG. 2). A load 314(e.g., a processor) is powered from output node Vo. Extended outputtongue 308 provides a low impedance path between inductor 300 and load314, despite height restriction 312 dictating that inductor 300 beplaced remote from load 314. If inductor 308 did not include extendedoutput tongue 308, current from inductor 300 to load 314 would typicallyhave to flow through a much higher impedance trace of PCB 302. Inductor300, however, is not limited to use in buck converter or even inDC-to-DC converter applications. For example, some embodiments ofinductor 300 could be used in inverter applications.

FIGS. 6 and 7 show one possible application of an embodiment of inductor300. In particular, FIG. 6 shows a side plan view and FIG. 7 shows a topplan view of one inductor 600, which is an embodiment of inductor 300,installed on a PCB 602. In the examples of FIGS. 6 and 7, inductor 600serves as a buck converter output inductor. Extended input tongue 604connects one end of a winding 606 to a DC-to-DC converter switching nodeVx, while a solder tab 608 connects the other end of winding 606 to aDC-to-DC converter output node Vo. Winding 606 is wound at leastpartially around or through at least a portion of a magnetic core 610.Dashed lines indicate the outline of winding 606 where obscured by core610. Extended input tongue 604 spans a significant portion of a distance702 between inductor 600 and a switching device 612, therebysignificantly lowering the impedance between switching device 612 andinductor 600. Such lowering of impedance may significantly decreasepower loss, as switching node Vx typically conducts a large currentmagnitude.

As the extended tongues discussed above (e.g., extended output tongue308 of FIG. 3, extended input tongue 502 of FIG. 5) may significantlyimprove electrical and thermal conductivity from switching devices(e.g., power semiconductors) towards the load in DC-to-DC converterapplications, the concept of paralleling a thick foil with thin PCBtraces can also be applied to ground return currents (i.e., currentsfrom the load back to the DC-to-DC converter). An issue with applyingnaked foils to PCB traces is that such foils can be difficult to handle.

One or more ground return conductors can be attached to an inductor toimprove ground return conductivity in the inductor's vicinity. Theground return conductors, for example, are configured and arranged suchthat their inductance is not significantly increased by presence of theinductor's core, while inductance of the inductor's winding (orwindings) is significantly increased by presence of the inductor's core,relative to an otherwise identical inductor without the core. As anexample, the ground return conductors may be configured and arrangedsuch that the inductor's core does not form a magnetic path loop aroundthe ground return conductors. In such embodiments, the ground returnconductors are external to core, and the ground return conductors mayhave an inductance similar to that of a PCB ground plane extending undera standard surface mount inductor (without ground return conductors),where the ground plane is in close proximity to the standard surfacemount inductor's core.

In many applications, current flows from switching devices through theinductor and to a load. Return current typically flows from the load,through PCB conductive layers under the inductor, and back to theswitching devices. Accordingly, use of an inductor including groundreturn conductors may reduce ground return path impedance whilemaintaining the PCB's general current flow path.

Additionally, attaching a ground return conductor to an inductor allowsboth the inductor and the ground return conductor to be placed in asingle step, thereby eliminating multiple placement operations requiredfor placement of a discrete inductor and a discrete conductor.Furthermore, applying a foil conductor to a PCB may be difficult due tothe foil's flexibility, but attaching a foil ground return conductor toan inductor increases the conductor's rigidity and may therebyfacilitate the conductor's placement on a PCB.

For example, FIG. 8 shows a side plan view of one inductor 800 installedon a PCB 802, and FIG. 9 shows a top plan view of inductor 800. Inductor800 includes ground return conductors 804, 806, in addition to a winding808 wound at least partially around or through at least a portion of amagnetic core 810. Dashed lines indicate the outline of winding 808 andground return conductors 804, 806 where obscured by core 810 in FIGS. 8and 9. Core 810 does not form a magnetic path loop around ground returnconductors 804, 806. Accordingly, inductance of ground return conductors804, 806 is not significantly increased by the presence of core 810, andground return conductors 804, 806 have a lower inductance than winding808. FIG. 10 shows a top perspective view of inductor 800 with core 810removed, and FIG. 11 shows a top plan view of one possible PCB footprintfor use with inductor 800.

In some embodiments, each end of ground return conductors 804, 806 andeach end of winding 808 form respective solder tabs at a same heightrelative to a bottom surface 816 of core 810 to facilitate surface mountconnection of inductor 800 to a PCB. Ground return conductors 804, 806,for example, have a thickness similar to that of winding 808 and aresignificantly thicker than foil typically forming a PCB ground returnplane. Accordingly, ground return conductors 804, 806 may be used tosupplement (or replace) a ground return conductor in a PCB (e.g., a PCB802), and thereby significantly reduce the ground return impedance inthe vicinity of inductor 800. Since ground-return conductors 804, 806are attached to core 810, and thus to inductor 800, they are easier tohandle than discrete conductors and may be positioned by pick-and-placeequipment simultaneously with positioning inductor 800.

Accordingly, inductor 800 may be used to provide a low impedance,two-way path for current between DC-to-DC converter (e.g., buckconverter) switching devices and a load, as shown in the examples ofFIG. 8-11. In particular winding 808 may carry current from a switchingnode Vx to an output node Vo, as shown by arrows 812. Ground returnconductors 804, 806 may in turn carry at least part of the ground returnfrom the load back to the switching devices, as shown by arrows 814.

The configuration and quantity of ground return conductors 804, 806 maybe varied, and examples of some variations are discussed below.Additionally, although inductor 800 is discussed in the context ofwinding 808 carrying current to a load and ground return conductors 804,806 carrying ground return current, inductor 800 could be used in othermanners. For example, one or more of ground return conductors 804, 806could be utilized to carry current, such as current from a memory-keepalive power supply (not shown) to the load, instead of ground returncurrent. Furthermore, inductor 800 is not limited to use in DC-to-DCconverter applications. For example, some embodiments of inductor 800could be used in inverter applications.

A variation of inductor 800 is shown in FIGS. 12-14. FIG. 12 is a sideplan view of one inductor 1200 installed on a PCB 1202, and FIG. 13 is atop plan view of inductor 1200. Inductor 1200 is similar to inductor 300of FIG. 3; however, inductor 1200 includes ground return conductors1204, 1206 in addition to a winding 1208 at least partially wound aroundor through at least a portion of a magnetic core 1210. Dashed linesindicate the outline of winding 1208 and ground return conductors 1204,1206 where obscured by core 1210. Ground return conductors 1204, 1206attach to a bottom surface 1216 of core 1210, and core 1210 does notform a magnetic path loop around ground return conductors 1204, 1206.Accordingly, inductance of ground return conductors 1204, 1206 is notsignificantly increased by presence of core 1210. An extended outputtongue 1302 is electrically coupled to winding 1208, and ground returnconductors 1204, 1206, for example, extend at least partially along alength 1304 of extended output tongue 1302. FIG. 14 shows a topperspective view of inductor 1200 with core 1210 removed. Portions ofground conductors 1204, 1206 are, for example, formed at the same heightas extended output tongue 1302 with respect to bottom surface 1216 ofcore 1210 to facilitate surface mount connection of inductor 1200 to aPCB. FIG. 12 shows one possible application of inductor 1200 whereextended output tongue 1302 and ground return conductors 1204, 1206provide a two way, low impedance path between inductor 1200 and a load1212 despite a height restriction 1214 dictating that inductor 1200 beplaced remote from load 1212.

FIGS. 15-17 show another variation of inductor 800. In particular, FIG.15 shows a side plan view of one inductor 1500 installed on a PCB 1502.FIG. 16 shows a top plan view, and FIG. 17 shows a top perspective viewof inductor 1500. Inductor 1500 is similar to inductor 1200 (FIGS.12-14), but inductor 1500 includes an extended input tongue 1504electrically coupled to a winding 1506. Ground return conductors 1508,1510 extend at least partially along a length 1602 of an extended outputtongue 1604. Winding 1506 is wound at least partially around or throughat least a portion of a magnetic core 1514. Dashed lines indicate theoutline of winding 1506 and ground return conductors 1508, 1510 whereobscured by core 1514 in the plan views of FIGS. 15 and 16. Core 1514 isshown as being transparent in FIG. 17. Extended output tongue 1604,extended input tongue 1504, and the portions of ground return conductors1508, 1510 extending along extended output tongue 1604 are, for example,formed at the same height relative to a bottom surface 1520 of core 1514to facilitate surface mount connection of inductor 1500 to a PCB.Inductor 1500 is, for example, used to provide a two way, low impedancepath between DC-to-DC converter switching devices and inductor 1500, aswell as between inductor 1500 and a load 1516 separated from inductor1500 by a height restriction 1518.

Some embodiments of inductors with an extended tongue (e.g., inductor300, FIG. 3) and inductors with ground return conductors (e.g., inductor800, FIG. 8) are multiple winding inductors with N windings, where N isan integer greater than one. For example, FIG. 18 shows a top plan viewof one coupled inductor 1800, which includes three windings 1802 whichare magnetically coupled together by a magnetic core 1804. Dashed linesindicate the outline of windings 1802 where obscured by core 1804. Arespective extended output tongue 1806 is electrically coupled to oneend of each winding 1802, and a respective extended input tongue 1808 iselectrically coupled to the other end of each winding 1802. Eachextended output tongue 1806 and each extended input tongue 1808 is, forexample, an extension of a respective winding 1802. FIG. 19 shows a topperspective view of one winding 1802.

At least portions of extended output tongues 1806 and extended inputtongues 1808 are, for example, formed at a same height relative to abottom surface of core 1804 to facilitate surface mount connection ofinductor 1800 to a PCB. Each extended output tongue 1806, for example,supplements or replaces a PCB trace connecting inductor 1800 to a load(e.g., a processor). Each extended input tongue 1808, for example,supplements or replaces a PCB trace connecting inductor 1800 to DC-to-DCconverter switching devices. Although FIG. 18 shows inductor 1800 asincluding three windings, inductor 1800 could have any number ofwindings greater than one. For example, FIG. 20 shows a top perspectiveview of a four winding embodiment of inductor 1800.

In some systems, each winding of a multiple winding inductor (e.g.,inductor 1800) may be part of a separate phase of a multiphase DC-to-DCconverter, such as discussed above with respect to FIG. 2.

FIG. 21 shows a top plan view of one coupled inductor 2100, which issimilar to inductor 1800 (FIG. 18); however, inductor 2100 includesground return conductors 2102 disposed along extended output tongues2104, where each extended output tongue 2104 is electrically coupled toa respective winding 2106. Ground return conductors 2102, for example,provide a low impedance ground return path between inductor 2100 andanother component (e.g., a load, such as a processor). Ground returnconductors 2102 as well as extended output tongues 2104 also may serveas heat sinks to cool a PCB that inductor 2100 is installed on. Dashedlines in FIG. 21 indicate outlines of windings 2106 and ground returnconductors 2102 obscured by a magnetic core 2108 of inductor 2100. Atleast respective portions of ground return conductors 2102, extendedoutput tongues 2104, and extended input tongues 2110 are, for example,formed at a same height relative to a bottom surface of inductor 2100 tofacilitate surface mount connection to a PCB.

It should be noted that the quantity of windings as well as the quantityand configuration of ground return conductors may be varied. Forexample, FIG. 22 is a top plan view and FIG. 23 is a side plan view ofone coupled inductor 2200, which is an embodiment of coupled inductor2100 including at least one mechanical isolator 2202 connected to atleast some of ground return conductors 2204 and/or extended outputtongues 2206. Isolator 2202 increases mechanical strength of inductor2200, as well as the planarity of ground return conductors 2204 and/orextended output tongues 2206. FIG. 23 shows inductor 2200 installed on aPCB 2302. Dashed lines indicate the outlines of windings and groundreturn conductors 2204 obscured by a magnetic core 2208 or isolator2202.

FIG. 24 is a top plan view of one coupled inductor 2400, FIG. 25 is aside plan view of coupled inductor 2400 installed on a PCB 2502, andFIG. 26 is a top perspective view of a four winding embodiment ofcoupled inductor 2400. Coupled inductor 2400 is similar to coupledinductor 2200 (FIG. 22). However, in contrast with coupled inductor2200, coupled inductor 2400's magnetic core 2402 does not includefeatures (e.g., gapped outer legs) to boost leakage inductance values.Instead, core 2402 and windings 2404 form a nearly-ideal transformer,and an area or channel 2502 formed by ground return conductors 2406 andextended output tongues 2408 serves as an “air core inductor” whichboosts the leakage inductance values of windings 2404. The air coreadvantageously has close to zero core losses. Isolator 2410 canoptionally be formed of a magnetic material (e.g., a ferrite and/or apowdered iron material) to increase the leakage inductance values ofinductor 2400. Such magnetic material could be selected such thatisolator 2410 at least partially saturates during normal operation ofinductor 2400, thereby resulting in a significant decrease in leakageinductance values at high but normal winding currents. Dashed linesindicate an outline of windings 2404 and ground return conductors 2406where obscured by core 2402 or isolator 2410.

FIG. 27 shows a top plan view of one coupled inductor 2700, and FIG. 28shows a side plan view of coupled inductor 2700 installed on a PCB 2802.Coupled inductor 2700 is similar to inductor 2400 (FIG. 24). However, ininductor 2700, ground return conductors 2702 and extended output tongues2704 are formed at least substantially at the same height with respectto magnetic core 2708 and do not form air core inductors. Isolator 2706is formed of a magnetic material, which may be selected such thatisolator 2706 at least partially saturates during normal operation ofinductor 2700, thereby resulting in a significant decrease in leakageinductance values at high but normal winding currents. Dashed linesindicate the outline of windings and ground return conductors 2702obscured by magnetic core 2708.

In other embodiments, low profile inductors as illustrated in FIG.29-32, 33-35, or 36-38 have a low resistance foil winding, which is forexample in part used to bridge the distance from a height-unrestrictedarea of a PCB to a load.

FIG. 29 shows a side plan view of one inductor 2900 having a low profileinstalled on a PCB 2902, and FIG. 30 shows a top plan view of inductor2900. Inductor 2900 includes an elongated foil winding 2904 disposedabove an elongated foil ground return conductor 2906. Ground returnconductor 2906 is, for example, configured such that it only partiallycontacts a PCB, as shown in FIG. 29. Isolators 2908, 2910 separatewinding 2904 and ground return conductor 2906 such that inductor 2900forms an area or channel 2912 that serves as an air core. Winding 2904and ground return conductor 2906 are, for example, at leastsubstantially parallel along channel 2912. One or more of isolators2908, 2910 may optionally include a magnetic material (e.g., a ferritematerial and/or a powdered iron material) to boost inductance ofinductor 2900. FIG. 31 is a top perspective view of inductor 2900 withisolators 2908, 2910 removed, and FIG. 32 is a top plan view of one PCBfootprint that could be used with inductor 2900. As shown in FIG. 29,one possible application of inductor 2900 is to bridge a heightrestriction 2914 in the vicinity of a load 2916.

FIG. 33 shows a side plan view of one inductor 3300 having a low profileinstalled on a PCB 3302, and FIG. 34 shows a top plan view of inductor3300. Inductor 3300 includes a foil winding 3304 disposed above a foilground return conductor 3306. Inductor 3300 includes at least onemagnetic section 3308 formed of a magnetic material (e.g., a ferritematerial and/or a powdered iron material) disposed on ground returnconductor 3306. Winding 3304 extends through an opening in each magneticsection 3308. Magnetic sections 3308 increase inductance of inductor3300, provide mechanical support, and cause inductor 3300 to be“shielded”. It may be advantageous for inductor 3300 to include a numberof smaller magnetic sections 3308 instead of one large magnetic sectionbecause smaller magnetic sections may facilitate manufacturability,resist cracking, and tolerate PCB flexing, while nevertheless providingsignificant collective core cross section, which helps minimize coreloss in switching power supply applications. Winding 3304 and groundreturn conductor 3306 are shown by dashed lines where obscured bymagnetic sections 3308 in FIGS. 33-34. FIG. 35 shows a top perspectiveview of inductor 3300 with magnetic sections 3308 removed. As shown inFIG. 33, one possible application of inductor 3300 is to bridge a heightrestriction 3310 in the vicinity of a load 3312.

FIG. 36 shows a side plan view of one low profile inductor 3600installed on a PCB 3602, and FIG. 37 shows a top plan view of inductor3600. Inductor 3600 includes a foil winding 3604 disposed between groundreturn conductors 3606, 3608. At least one magnetic section 3610 (e.g.,formed of a ferrite material and/or a powdered iron material) isdisposed between ground return conductors 3606, 3608. Winding 3604 iswound through an opening in each magnetic section 3610 in FIGS. 36-37.For the same reasons as discussed above with respect to inductor 3300(FIGS. 33-35), it may be advantageous for inductor 3600 to include anumber of smaller magnetic sections 3610 instead of one large magneticsection. The outlines of winding 3604 and ground return conductors 3606,3608 are shown by dashed lines where obscured by magnetic sections 3610.FIG. 38 shows a top perspective view of inductor 3600 with magneticsections 3610 removed. Inductor 3600 may allow for use of larger crosssection magnetic sections than inductor 3300 due to ground returnconductors 3606, 3608 being disposed only on the sides of inductor 3600,which allows magnetic sections 3610 to occupy the portion of inductor3600's height that would otherwise be occupied by ground returnconductors. As shown in FIG. 36, one possible application of inductor3600 is to bridge a height restriction 3612 in the vicinity of a load3614.

State of the art switching devices generally have a height of less thanone millimeter when assembled on a PCB. Other commonly used surfacemount components, such as ceramic capacitors, also have a similarly lowheight. Inductors, however, typically have a height of severalmillimeters so that their cores have a sufficiently large cross sectionto keep core losses to an acceptable level.

Accordingly, in height restricted applications, it may be desirable touse a “drop-in” inductor disposed in a PCB aperture. For example, FIG.39 shows a side cross-sectional view of a prior art drop-inductor 3900installed in an aperture 3902 of a PCB 3904. Inductor 3900 includessolder tabs 3906, a magnetic core 3908, and a soft, multi-turn wirewinding (not shown in FIG. 39) wound around core 3908 and connected tosolder tabs 3906.

Inductor 3900 advantageously utilizes the height on both sides of PCB3904, as well as the thickness of PCB 3904. However, the aperturerequired for drop-in inductor 3900 reduces the path for return currentthrough ground plane or interconnect layers of the PCB in the vicinityof the inductor, thereby increasing the return path impedance andassociated losses. For example, FIG. 40 shows a top plan view ofinductor 4000 installed in aperture 3902 of PCB 3904. Return currentcannot flow through aperture 3902 —accordingly, return current must flowaround aperture 3902, as represented by arrows 4002, which increasesreturn path impedance. Accordingly, with typical drop-in inductors,sufficient space must be provided around aperture 3902 for returncurrent conduction. Additionally, inductance is affected by the returncurrent path, and aperture 3902 will affect the inductance of inductor3900 because return current does not flow under inductor 3900. Thesituation may be amplified in multiphase applications, such as shown inFIG. 41, where a plurality of apertures 4102 in a PCB 4104 are requiredfor prior art drop-in inductors 4100. Apertures 4102 significantlyincrease return path impedance, and significant spacing 4106 betweenapertures 4102 is required to provide a return current path.

Furthermore, inductor 3900 is often fragile when installed in a PCBaperture. In particular, inductor 3900's solder tabs 3906 typicallysupport inductor 3900's entire weight because inductor 3900's core 3908typically does not contact PCB 3904. Accordingly, solder tabs 3906 aretypically subject to significant mechanical stress, and may cause core3908, which is typically formed of a relatively fragile magneticmaterial, to crack.

At least some of the problems discussed above can be reduced oreliminated with a drop-in inductor including one or more ground returnconductors. For example, FIG. 42 shows a side cross-sectional view andFIG. 43 shows a top plan view of one drop-in inductor 4200 installed inan aperture of a PCB 4202. FIG. 44 shows a top perspective view ofinductor 4200.

Inductor 4200 includes a winding 4204 wound at least partially around orthrough at least a portion of a magnetic core 4206 (e.g., formed of aferrite and/or powdered iron material). Winding 4204, for example,extends through a channel in core 4206. FIG. 45 shows a top perspectiveview of inductor 4200 with core 4206 removed. Inductor 4200 alsoincludes ground return conductors 4208, 4210. Outlines of winding 4204and ground return conductors 4208, 4210 are shown by dashed lines inFIG. 43 where obscured by core 4206, and core 4206 is shown astransparent in FIG. 44. Winding 4204 and/or ground return conductors4208, 4210 are, for example, foil conductors, as shown in FIGS. 42-45.Such foil conductors may, but need not be, sufficiently thick to berelatively rigid. Core 4206 does not form a magnetic path loop aroundground return conductors 4208, 4210. Accordingly, inductance of groundreturn conductors 4208, 4210 is, for example, not significantlyincreased by presence of core 4206.

Inductor 4200 can be used, for example, to provide a path for returncurrent, as shown by arrows 4304 in FIG. 43, as well as to provide apath for current to a load, as shown by arrow 4306. Thus, in contrast toprior art drop-in inductors, return current does not need to flow aroundinductor 4200—instead return current can flow through ground returnconductors 4208, 4210 attached to inductor 4200.

In contrast to prior art drop-in inductors, use of inductor 4200 doesnot necessarily increase return path impedance. Ground return conductors4208, 4210 are often of similar thickness to that of winding 4204 andare frequently ten to fifty times thicker than typical PCB trace foilthickness. Use of drop-in inductor 4200 may therefore significantlydecrease return path impedance, despite a PCB aperture being requiredfor inductor 4200. Furthermore, inductance of inductor 4200 is lessaffected by PCB layout than prior art drop-in inductors because returncurrent flows through inductor 4200.

Moreover, because inductor 4200 provides a path for return current, anumber of inductors 4200 can be spaced close together without having toallow for space between inductors for a return current path, such asspacing 4106 required between prior art drop-in inductors 4100 of FIG.41. Ground return conductors 4208, 4210 may even allow a number ofinductors 4200 to be placed in a single aperture. Accordingly, a numberof inductors 4200 may require less space on a PCB than the same numberof prior art drop-in inductors because inductors 4200 can be placedcloser together than the prior art drop-in inductors, or a number ofinductors 4200 can be placed in a common aperture.

Winding 4204 and ground return conductors 4208, 4210, for example, haverespective solder tabs 4302 electrically coupled to their ends tofacilitate surface mount connection of inductor 4200 to a PCB. Soldertabs 4302 are typically formed at the same height relative to a bottomsurface 4212 of core 4206 to facilitate surface mount connection ofinductor 4200 to a PCB. In some embodiments, solder tabs 4302 areextensions of winding 4204 or ground return conductors 4208, 4210, whichmay facilitate manufacturability of inductor 4200. For example, winding4204 and its respective solder tabs 4302 may be formed of a single foilwinding. Each of solder tabs 4302, for example, connect to PCB traces ona common PCB layer.

Inductor 4200 may be more mechanically robust than prior art drop-ininductors. For example, in embodiments where winding 4204 is arelatively rigid foil extending through a channel in core 4206, winding4204 may provide significant mechanical support for inductor 4200. Incontrast, the soft, multi-turn wire winding of prior art drop-ininductor 3900 typically provides little to no mechanical support forinductor 3900.

Additionally, ground return conductor 4208, 4210 may increase mechanicalrobustness of inductor 4200. For example, solder tabs 4302 coupled toground return conductors 4208, 4210 may provide additional points tosupport inductor 4200 on a PCB, thereby reducing stress on inductor4200's solder tabs and consequently reducing the likelihood of core 4206cracking. For example, if each of winding 4204 and ground returnconductors 4208, 4210 have respective solder tabs 4302 coupled to theirends, inductor 4200 may be supported on a PCB at six different places,as opposed to prior art inductor 3900, which is supported at only twoplaces. Furthermore, ground return conductors 4208, 4210 may promoteoverall mechanical strength of inductor 4200.

Drop-in inductors with ground return conductors may have otherconfigurations. For example, FIG. 46 shows a top perspective view of onedrop-in inductor 4600, which is a variation of inductor 4200 (FIGS.42-45). Inductor 4600 includes a winding 4602 wound at least partiallyaround or through at least a portion of a magnetic core 4604 (shown astransparent in FIG. 46). Inductor 4600 further includes ground returnconductors 4606, 4608. FIG. 47 is an exploded perspective view ofinductor 4600 with magnetic core 4604 removed. A respective solder tab4610 may be electrically coupled to each end of winding 4602 and groundreturn conductors 4606, 4608. Each of solder tabs 4610 are, for example,formed at the same height relative to a bottom surface of core 4604 tofacilitate surface mount connection of inductor 4200 to a PCB.

Ground return conductors 4606, 4608 respectively include clamps 4612,4614 which may allow for easier clamping of the ground return conductorsto magnetic core 4604. Clamps 4612, 4614 may also increase robustness,physical attachment strength, and heat sinking ability of ground returnconductors 4606, 4608. FIGS. 48 shows a top perspective view of inductor4800, which is an alternate embodiment of inductor 4600 including groundreturn conductors 4802, 4804 that provide enhanced clamping to magneticcore 4806 and enhanced conductivity. Winding 4808 is wound at leastpartially around or through at least a portion of core 4806, and core4806 is shown as transparent in FIG. 48. FIG. 49 is an explodedperspective view of inductor 4800 with magnetic core 4806 removed.

The concept of adding ground return conductors to drop-in inductors canbe extended to inductors including multiple, magnetically coupledwindings. For example, FIG. 50 shows a top perspective view of a drop-incoupled inductor 5000 including ground return conductors 5002, 5004.Coupled inductor 5000 further includes windings 5006, 5008 wound atleast partially around or through at least a portion of a magnetic core5010 (shown as transparent in FIG. 50). FIG. 51 is a top perspectiveview of inductor 5000 with magnetic core 5010 removed. A respectivesolder tab 5012 is, for example, electrically coupled to each of groundreturn conductors 5002, 5004, and windings 5006, 5008. Solder tabs 5012are, for example, formed at the same height relative to a bottom surface5014 of core 5010 to facilitate surface mount connection of inductor5000 to a PCB. Although inductor 5000 is shown as being a two windingcoupled inductor, inductor 5000 could be extended to support three ormore windings. Additional ground return conductors could also be added,or ground return conductors 5002, 5004 could be combined into a singleconductor.

FIG. 52 shows a top plan view of one PCB assembly 5200, which shows onepossible application of coupled inductor 5000. In assembly 5200, notonly do windings 5006, 5008 respectively carry current from power stages5202, 5204 to a load, ground return conductor 5004 also carries currentto the load. Ground return conductor 5002, however, serves to carryreturn current.

FIG. 53 shows a top perspective view of one N-winding coupled inductor5300, which is another example of a drop-in inductor including a groundreturn conductor. Inductor 5300 includes N windings 5302, where N is aninteger greater than one. Although inductor 5300 is shown as includingfour windings, inductor 5300 could be modified to include any number ofwindings greater than one. Each winding 5302 is at least partially woundaround a respective leg of a magnetic core 5304. A respective solder tab5306 is electrically coupled to each end of each winding 5300. Soldertabs 5306 allow windings 5302 to be soldered to a PCB that inductor 5300is installed in an aperture of. Solder tabs 5306 are, for example,extensions of their respective windings 5302. FIG. 54 shows a topperspective view of windings 5302.

Inductor 5300 further includes a ground return current conductor in theform of a return current structure 5308 to provide a low impedance pathfor return current. FIG. 55 shows a top perspective view of structure5308. Structure 5308 can also advantageously serve as a heat sink forinductor 5300 and a PCB that inductor 5300 is installed in. Structure5308 includes, for example, several solder tabs 5310 for soldering to aPCB. Solder tabs 5306 and 5310 are, for example, formed at the sameheight relative to a bottom surface 5312 of core 5304 to facilitatesurface mount connection of inductor 5300 to a PCB. Structure 5308optionally includes an isolator 5502 to prevent structure 5308 fromelectrically shorting to windings 5302. Isolator 5502 is, for example, adielectric coating or an isolating layer, such as dielectric tape. Inthe example of FIG. 53, structure 5308 is disposed on the bottom side ofinductor 5300—accordingly, only solder tabs 5310 of structure 5308 arevisible in FIG. 53.

FIG. 56 shows an example of one possible application of inductor 5300.In particular, FIG. 56 is a side cross-sectional view of inductor 5300installed in an aperture of a PCB 5602. The vertical position ofinductor 5300 with respect to PCB 5602 could be varied by changing thedimensions of windings 5302 and structure 5308.

Although return current structure 5308 is disposed on the bottom side ofinductor 5300 in FIGS. 53 and 56, structure 5308 could alternately bedisposed on the top side of inductor 5300, as shown in FIG. 57. Placingstructure 5308 on the top side advantageously offers a flat (orsubstantially flat) surface to permit pick and place installation ofinductor 5300 without a top side label. Placing structure 5308 on thetop side of inductor 5300 may also facilitate cooling when there is moreair flow on a particular side of the PCB.

Although structure 5308 is shown as a ground current return conductor,it could be modified to carry additional signals. For example, analternate embodiment of structure 5308 includes two electricallyisolated electrical conductors, where one conductor serves as a groundreturn conductor, and the other conductor serves as a low current powersupply conductor (e.g., a conductor for a keep-alive power supply).

FIG. 58 shows a top perspective view of one drop-in N-winding coupledinductor 5800, where N is an integer greater than one. Inductor 5800 issimilar to inductor 5300 (FIG. 53); however windings 5802 of inductor5800 have a shorter length and thus a lower resistance than windings5302 of inductor 5300. FIG. 59 shows a top perspective view of onewinding 5802 which is, for example, symmetrical in order to reducewinding length. Inductor 5800 includes a magnetic core 5804, and arespective solder tab 5806 is electrically coupled to each end of eachwinding 5802. Similar to inductor 5300, inductor 5800 includes a groundreturn structure 5808, which, for example, includes several solder tabs5810. Solder tabs 5806 and 5810 may be formed at the same heightrelative to a bottom surface 5812 of core 5804 to facilitate surfacemount connection of inductor 5800 to a PCB.

Core 5804 is, for example, formed of pairs of corresponding magneticelements 5814, 5816 and 5818, 5820, as shown in FIG. 58. In suchembodiments, solder tabs 5806 extend from spaces between correspondingmagnetic elements 5814, 5816 and 5818, 5820. In embodiments wherewindings 5802 are symmetrical, each of corresponding magnetic elements5814, 5816 and 5818, 5820 have, for example, an identical shape andsize.

FIG. 60 shows an example of one possible application of inductor 5800.In particular, FIG. 60 is a side cross-sectional view of inductor 5800installed in an aperture of a PCB 6002. The vertical position ofinductor 5800 with respect to PCB 6002 could be varied by changing thedimensions of windings 5802 and structure 5808. Although ground returnstructure 5808 is installed on the bottom side of inductor 5800 in FIGS.58 and 60, structure 5808 could be installed on the top side of inductor5800, as shown in FIG. 61.

As discussed above, use of prior art drop-in inductors typically resultsin problems including significantly increased return current pathimpedance, poor mechanical robustness, and the need to separate multipleinstances of the prior art drop-in inductors. However, drop-in inductorswith ground return conductors, such as some embodiments of the inductorsdiscussed above, may reduce or eliminate one or more of these problems,as previously discussed. Accordingly, the addition of ground returnconductors to drop-in inductors may allow for use of drop-in inductorsin applications where prior art drop-in inductors would be impractical.Use of drop-in inductors instead of standard (non drop-in) surface mountinductors may offer a number of advantages, such as the following: (1)reduced inductor height relative to the PCB surface; (2) increasedinductor core size and cross section, which helps minimize core loss;(3) reduced PCB surface area required for the inductors; and/or (4)inductor height being closer to that of other power supply components,resulting in improved power supply volume utilization.

Adding one or more ground return conductors to a drop-in inductor mayalso significantly reduce or eliminate inductance dependence on layoutand/or PCB aperture configuration. In particular, adding one or moreground return conductors to a drop-in inductor helps minimize length ofthe inductor's current loop in output inductor applications, where thecurrent loop is defined by the path current takes when flowing throughthe inductor to a load, and from the load back by the inductor.Inductance is affected by the current loop's configuration, andincreasing the current loop's size generally increases inductance.Accordingly, by minimizing current loop length through use of groundreturn conductors, current loop length may be significantly orcompletely unaffected by PCB layout and/or aperture configuration,thereby reducing or eliminating inductance dependence on suchapplication characteristics. In contrast, in the prior art drop-ininductor of FIGS. 39-41, current loop size is significantly dependent onPCB layout and aperture configuration. For example, in the case of priorart inductor 3900 (FIGS. 39-40), inductor 3900's inductance will changeif the size of aperture 3902 or the PCB layout around aperture 3902 ischanged.

FIGS. 62-64 respectively show a perspective, a side plan, and a top planview of an inductor 6200. Inductor 6200 is similar to inductor 500 (FIG.5), but with foil extended input and output tongues 6202, 6204 of atleast substantially the same length. Inductor 6200 includes a foilwinding 6206 and a core 6208 formed of magnetic material. Core 6208 hasa first side 6210 opposite to a second side 6212. A linear separationdistance between first and second sides 6210, 6212 of core 6208 definesa length 6214 of core 6208.

Foil winding 6206 including a core winding portion 6216 wound throughcore 6208. Extended input and output tongues 6202, 6204 are electricallycoupled to opposite respective ends of foil winding 6206. In certainembodiments, input and output tongues 6202, 6204 are each an extensionof winding 6206. Input tongue 6202 is at first side 6210 of core 6208and extends away from core 6208 in a lengthwise direction 6218, andoutput tongue 6204 is at second side 6212 of core 6208 and extends awayfrom core 6208 in lengthwise direction 6218. Dashed lines indicate theoutline of winding 6206 where obscured by core 6208. Extended input andoutput tongues 6202, 6204, for example, supplement or serve as asubstitute for respective foil traces disposed on a surface of a printedcircuit board. For example, one or more of input and output tongues6202, 6204 may be configured for soldering to and extending alongrespective PCB foil traces.

Extended input tongue 6202 has a length 6220, and extended output tongue6204 has a length 6222. Length 6220 is at least substantially equal tolength 6222. In certain embodiments, each of lengths 6220, 6222 oftongues 6202, 6204 are less than length 6214 of core 6208. Each oftongues 6202, 6204 are formed at a same height relative to a bottomsurface 6224 of core 6208 to facilitate surface mount soldering oftongues 6202, 6204 to a PCB.

FIGS. 65-67 respectively show a perspective, a side plan, and a top planview of an inductor 6500, which is an alternate embodiment of inductor6200 (FIGS. 62-64), and includes two ground return conductors 6502,6504. Inductor 6500 is similar to inductor 1500 (FIGS. 15-17), but withground return conductor extensions and extended input and output tonguesof at least substantially equal length. Ground return conductors 6502,6504 attach to bottom surface 6224 of core 6208, and core 6208 does notform a magnetic path loop around ground return conductors 6502, 6504.Accordingly, inductance of ground return conductors 6502, 6504 is notsignificantly increased by presence of core 6208, while inductance ofwinding 6206 is increased by presence of core 6208, relative to anotherwise identical inductor without core 6208. As can be seen in FIGS.65 and 67, ground return conductors 6502, 6504 are each adjacent foilwinding 6206 in lengthwise direction 6218.

Both of ground return conductors 6502, 6504 include a respective firstextension 6506, 6508 at first side 6210 of core 6208 and extending awayfrom core 6208 in lengthwise direction 6218. Similarly, both of groundreturn conductors 6502, 6504 includes a respective second extension6510, 6512 at second side 6212 of core 6208 and extending away from core6208 in lengthwise direction 6218. Each extension 6506, 6508, 6510,6512, as well as extended input and output tongues 6202, 6204, areformed at a same height relative to bottom surface 6224 of core 6208 tofacilitate surface mount soldering to a PCB. Each first extension 6506,6508 has the same length 6220 as extended input tongue 6202, and eachsecond extension 6510, 6512 has the same length 6222 as extended outputtongue 6204. As discussed above, each of extended input and outputtongues 6202, 6204 has the same length, and each extension 6506, 6508,6510, 6512 therefore has the same length as each tongue.

FIG. 68 shows a perspective view of an inductor 6800, which is similarto inductor 6500 (FIGS. 65-67), but with an alternative ground returnconductor configuration. Inductor 6800 includes ground return conductors6802, 6804, which are similar to the ground return conductors ofinductor 6500, but extend up at least partially along sides 6210, 6212,6806, 6808 of core 6208, as shown in FIG. 68. Such extensions of groundreturn conductors 6802, 6804 along sides of core 6208 advantageouslypromote mechanical robustness of inductor 6800 and also increase theeffective cross sectional area of ground return conductors 6802, 6804.Increased ground return conductor 6802, 6804 cross sectional areapromotes low impedance of the ground return conductors, as well ascooling of inductor 6800 and a PCB in contact with inductor 6800.Furthermore, the portions of ground return conductors 6802, 6804 thatextend along sides of core 6208 are exposed (i.e., do not contact a PCB)in typical applications, and therefore are particularly effective incooling inductor 6800.

In certain embodiments of the inductors disclosed herein, the core isfoamed of a powder magnetic material, such as powdered iron within abinder, and the one or more windings are at least partially embedded inthe core. For example, FIG. 69 shows a perspective view of inductor6900, which is similar to inductor 6200 (FIGS. 62-64), but with foilcore winding portion 6216 replaced with a wire core winding portion 6902embedded in core 6208. As another example, FIG. 70 shows a perspectiveview of inductor 7000, which is similar to inductor 6500 (FIGS. 65-67),but with foil core winding portion 6216 replaced with a wire corewinding portion 7002 embedded in core 6208.

It is anticipated that the foil windings and ground return conductorsdescribed herein are considerably thicker, and thereby offerconsiderably lower sheet resistivity, than the one-ounce copper foilused on many printed circuit boards. It is further anticipated that thefoil windings and ground return conductors described herein are madefrom a highly conductive material comprising primarily copper. Inalternative embodiments, the foil windings and ground return conductorsare made from a non-cuprous metal such as aluminum or steel having asolderable low resistance coating of copper, and is-may in turn beplated with tin or an alloy comprising tin for enhanced solderability.

Changes may be made in the above methods and systems without departingfrom the scope hereof. It should thus be noted that the matter containedin the above description or shown in the accompanying drawings should beinterpreted as illustrative and not in a limiting sense. The followingclaims are intended to cover all generic and specific features describedherein, as well as all statements of the scope of the present method andsystem, which, as a matter of language, might be said to falltherebetween.

1. An inductor for assembly on a printed circuit board, comprising: acore formed of a magnetic material, the core having a first side and asecond side opposite to the first side, a linear separation distancebetween the first and second sides of the core defining a length of thecore; and a winding including: (a) a core winding portion wound throughthe core, (b) a foil input tongue at the first side of the core andextending away from the core in the lengthwise direction, and (c) a foiloutput tongue at the second side of the core and extending away from thecore in the lengthwise direction; wherein at least a portion of the foilinput tongue and a portion of the foil output tongue are formed at asame height relative to a bottom surface of the core for surface mountattachment to the printed circuit board, the height being generallyperpendicular to the lengthwise direction.
 2. The inductor of claim 1,wherein: a portion of the foil input tongue is configured for solderingto and extending along a first foil trace of the printed circuit board;and a portion of the foil output tongue is configured for soldering toand extending along a second foil trace of the printed circuit board. 3.The inductor of claim 1, wherein each of the foil input and outputtongues has a different length.
 4. The inductor of claim 1, wherein eachof the foil input and output tongues are at least substantially the samelength.
 5. The inductor of claim 4, further comprising: a first groundreturn conductor attached to the core and adjacent the winding in thelengthwise direction; and a second ground return conductor attached tothe core and adjacent the winding in the lengthwise direction, whereinthe winding and the first and second ground return conductors areconfigured such that inductance of the first and second ground returnconductors is not significantly increased by presence of the core, whileinductance of the winding is significantly increased by presence of thecore, relative to an otherwise identical inductor without the core. 6.The inductor of claim 5, wherein opposing ends of both the first andsecond ground return conductors are configured for surface mountattachment to the printed circuit board.
 7. The inductor of claim 6,wherein: the first and second ground return conductors both includerespective first extensions at the first side of the core and extendingaway from the core in the lengthwise direction; and the first and secondground return conductors both include respective second extensions atthe second side of the core and extending away from the core in thelengthwise direction.
 8. The inductor of claim 7, wherein one of therespective first and second extensions has a different length than theother of the respective first and second extensions.
 9. The inductor ofclaim 7, wherein: both of the foil input and output tongues have atleast substantially the same length; and each of the respective firstand second extensions has at least substantially the same length as acorresponding adjacent one of the foil input and output tongues.
 10. Theinductor of claim 7, wherein at least a portion of each of therespective first and second extensions, the foil input tongue, and thefoil output tongue are displaced from the bottom surface of the coresuch that the inductor may function as a drop-in inductor.
 11. Theinductor of claim 1, wherein: a length of the foil input tongue is lessthan the length of the core; and a length of the foil output tongue isless than the length of the core.
 12. The inductor of claim 11, furthercomprising: a first ground return conductor attached to the core andadjacent the winding in the lengthwise direction; and a second groundreturn conductor attached to the core and adjacent the winding in thelengthwise direction, wherein the winding and the first and secondground return conductors are configured such that inductance of thefirst and second ground return conductors is not significantly increasedby presence of the core, while inductance of the winding issignificantly increased by presence of the core, relative to anotherwise identical inductor without the core.
 13. The inductor of claim12, wherein each of the foil input and output tongues are at leastsubstantially the same length.
 14. The inductor of claim 13, whereinopposing ends of both the first and second ground return conductors areconfigured for surface mount attachment to the printed circuit board.15. The inductor of claim 14, wherein: the first and second groundreturn conductors both include respective first extensions at the firstside of the core and extending away from the core in the lengthwisedirection; and the first and second ground return conductors bothinclude respective second extensions at the second side of the core andextending away from the core in the lengthwise direction.
 16. Theinductor of claim 15, wherein one of the respective first and secondextensions has a different length than the other of the respective firstand second extensions.
 17. The inductor of claim 15, wherein: both ofthe foil input and output tongues have at least substantially the samelength; and each of the respective first and second extensions has atleast substantially the same length as a corresponding adjacent one ofthe foil input and output tongues.
 18. The inductor of claim 15, whereinat least a portion of each of the respective first and secondextensions, the foil input tongue, and the foil output tongue aredisplaced from the bottom surface of the core such that the inductor mayfunction as a drop-in inductor.